A DVD disc contains a small lead-in area that contains sync sectors, control data including the number of recording surfaces, disc keys and other information, and contains a data area occupying the main part of the available disc surface. In order to handle the content of a DVD Video disc it is necessary to transform a logical sector number denoted LSN into a physical sector number denoted PSN. A DVD disc may contain up to four recording surfaces.
If there is more than one recording surface to be accessed, U.S. Pat. No. 5,966,721 discloses how to make the content of the lead-in areas of multiple recording surfaces readable from one surface only.